1. Field of the Invention
The present invention relates to a method for forming from a mold optical articles, in particular ophthalmic articles such as ophthalmic lenses, having a hydrophobic top coat thereon.
2. Previous Art
It is a common practice in the art to coat at least one face of an ophthalmic lens with several coatings for imparting to the finished lens additional or improved optical or mechanical properties. Thus, it is usual practice to coat at least one face of an ophthalmic lens substrate typically made of an organic glass material with successively, starting from the face of the substrate, an impact-resistant coating (impact-resistant primer), a scratch-resistant coating (hard coat), an anti-reflecting coating and a hydrophobic top coat.
Typically, optical articles made of organic glass materials are formed in a mold comprising two separate parts having optical surfaces which, when the two-parts are assembled, define a molding cavity. A liquid curable composition is then introduced in the molding cavity and cured to form the optical article. The optical article is thereafter recovered upon disassembling of the mold parts.
Examples of typical two-part molds and molding methods are disclosed in U.S. Pat. Nos. 5,547,618 and 5,662,839.
It is known in the art to also apply a scratch-resistant coating composition on the optical surfaces of the parts of a two-part mold, and if necessary precure it, assemble the mold parts, fill the molding cavity with an optical liquid curable material, cure the optical material and disassemble the mold parts to recover the molded optical article having a scratch-resistant coating deposited and adhered thereon.
Such a method is, for example, disclosed in document EP-102847.
U.S. Pat. No. 5,096,626 discloses a method for making an optical article having a scratch-resistant coating and/or an anti-reflecting coating thereon, which comprises:                forming an anti-reflecting coating and/or a scratch-resistant coating onto the optical surfaces of a two-part mold;        assembling the two-part mold;        pouring an optical liquid curable composition in the molding cavity;        curing the optical composition, and        disassembling the two-part mold for recovering the molded optical article having a scratch-resistant coating or a scratch-resistant coating and an anti-reflecting coating thereon;wherein, either at least one release agent is incorporated into the scratch-resistant coating or a film of at least one release agent is formed on the optical surfaces of the mold parts, prior to the formation of the anti-reflecting coating and/or the scratch-resistant coating.        
The preferred release agents useful in the method of U.S. Pat. No. 5,096,626 are fluorosilicones, fluoroalkyalkoxysilanes and mixtures thereof.
U.S. Pat. No. 5,160,668 discloses a method for transferring an anti-reflecting coating onto a surface of an optical element which comprises:                forming on the optical surface of a part of a two-part mold a release layer of a water soluble inorganic salt;        forming on said release layer an anti-reflecting layer,        assembling the mold parts;        pouring a liquid optical curable composition in the molding cavity,        curing the optical composition,        disassembling the mold parts and dissolving the release layer in water to recover the coated optical element.        
U.S. Pat. No. 5,733,483 discloses a method for forming on-site tinted and coated optical elements from a mold which comprises:                forming successively on an optical surface of at least one part of a two-part mold, a polymer release layer, an anti-reflecting coating layer, a coupling agent layer and a hard coat layer;        assembling the two-part mold;        pouring an optical liquid curable material in the molding cavity;        curing the optical material and the anti-reflecting, coupling agent and hard coat layers; and        disassembling the mold parts to recover the coated optical element.        
The polymer release layer can be made of a water soluble polymer such as polyvinylic acid (PAA), polyethylene-oxide (PEO), poly(N-vinylpyrolidone) (PNVP), polyvinylalcohol (PVA) or polyacrylamid (PAM); a non-water soluble and UV curable polymer such as polybutadiene-diacrylate (PBD-SA), polyethyleneglycol-diacrylate (PEG-DA) or a highly crosslinked acrylate, and commercial mold release agents such as Dow-Corning 20 Release.
The coupling agent layer generally comprises a (meth)acryloxyalkyltrialkoxysilane. This coupling agent layer is used in order to better extract the anti-reflecting coating from the mold.
Hydrophobic top coats are classically used for improving dirty mark resistance of finished optical articles, in particular optical articles comprising an anti-reflecting coating.
A problem associated with these hydrophobic top coats is their tendency to poorly adhere on the optical substrate and in particular on the anti-reflecting coating of a coated optical substrate.
What is needed is a method which will provide easy transfer from a mold of a hydrophobic top coat onto an optical substrate, in particular onto the anti-reflecting coating of a coated optical substrate as well as an improved adhesion of the hydrophobic top coat onto the optical substrate and in particular onto the anti-reflecting coating of a coated optical substrate.